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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Thu 05, 2004 8:39 pm 
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Location: ayer ,ma usa
After fixing many of them,I have noticed really large variations in performance of AA5's. It is odd, that with the same basic circuit and tubes, that they vary so much. A person would not be aware of this unless he/she has repaired 40-50 of them...you just can't believe the spread! I doubt it could be variation in restoration, or tubes,although I have been paying more attention to "zeroing"the dial and tuning cap as the instructions tell you to , mechanically,before adjusting any tuning trimmers. Failure to do that FIRST causes mistracking, usually a radio the is "HOT' above 1100 kc and dead below 850. I have also been noting more carefully that just about every radio, especially Philco, have those segmented tuning plates on the ends of the tuning gang, and they are almost always bent out /adjusted. The factory must have had a protocol to do that, and it ought to be still correct, (so don't try to improve it!)but Zenith are seldom bent, and whether related, seem to have the worst performance. Crosleys are also very good performers,in my experience, while RCA leaves a lot to be desired, like Zenith.I just finished a Delco AA5 that had a failed IF that I had to get into ,one of those soldered shut boxes under the chassis, and only one trimmer (strange) ;inside, the two coils were wound together(bifiliar),indicating high coefficient of coupling, which ought to give poor selectivity,but high gain.(like a TRF coil) 2nd IF was normal type; the wire had opened, but luckily ,this time it was outer turns(whew); what surprised me was this tiny radio is one of the best AA5's I ever touched(their auto radio experience?) and no problems with selectivity ; maybe the conventional IF design is not the best one? A tiny Philco with all loctals was done at the same time.Delco is MUCH better,especially in sensitivity and max volume out without distortion, on an A-B side by side comparison. I wonder if 50L6 is in fact better than 35 volt version, or loctal version? how can 35 V heater be as powerful as 50V? 25L6 is also very good sounding in earlier radios, much better than 43's.I notice some RCA's have a "gain per stage metric"("120X") above the circuit print..must be for some kind of RCA test setup, but maybe we should find a way to do that, say with a scope(easy today). I am thinking of pulling apart (for 3rd time)a real nice looking wooden Zenith AA5 I have gone thru twice that is a better doorstop than radio, despite my best efforts, and try to find out why? Anyone else notice this stuff??It can drive you nuts, unless you believe in "Lemons" ; I am starting to...<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Thu 05, 2004 9:00 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34326
Location: Sandpoint, IDAHO 83864
Well, if it will help any, I can remember when I was a kid that anybody in the market for a radio (which were all of the AA5 types- mid 60's), the first question any hopeful customer would ask was "will it pick up the stations in Spokane?" I am referring to Spokane, Washington, as I live in North Idaho about 60 to 70 airline miles from the towers on Tower Mountain.<BR>I can still remember vast differences among the various inexpensive sets. It seemed our family favorites were always Packard-Bell sets, as they could pull in the stations clearly. Yes, I do recall one particular Zenith AA5 set that the guy from the radio repair shop brought by to have my folks try it out. (This particular shop repaired and sold new sets). The Zenith had to be one of the sickest sets ever! So, I must agree with your conclusions.<BR>Curt<P>------------------<BR>Curt, N7AH


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Thu 05, 2004 9:11 pm 
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They are definitely not all the same in performance. Some of it is in the design.<BR>Usually Zeniths are among the best, there might be some issue remaining with the one you mentioned. I have found several of them with cap problems in the IF cans where there was no static caused by leakage across the mica, and the trimmer adjustments appeared to work. But removing the mica plate and installing the correct value of silver mica caps and then realigning corrected the problem.<P>Having repaired literally thousands of AA5's over the years, I concur with the importance of proper alignment following the original manufacturers instructions. Those slotted outer plates on the tuning gang were designed to set the tracking across the full rotation and were bent in or out at various specific dial settings, not just at the ends. But the exact method used at the factory is probably lost forever, very few mention it in the service data. <P>The 35L6 is not the electrical equivalent of the 50L6 although the 50L6 is frequently used as a sub. The characteristics in the tube manual for the 35L6 are markedly different. The 50L6 is equivalent to the 25L6, except for the heater voltage difference. All of those are beam power tubes, and do sound better than pentodes like the 43.<P>------------------<BR>Dennis


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Thu 05, 2004 9:21 pm 
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Location: Livermore, CA
Hi<P> Agree there are differences. There is a gain difference between 43 & 25L6 tubes but this isn't the entire answer. Don't think it 35L6 vs. 50L6 either.<P> Could it be IF transformer differences? Those small IF Transformers with mica caps built in usually end up in good performance radios. I've used these small IF's in place of larger ones and performance was better than I expected.<P> Ferrite used in these IF transformers is more effecient than air core, higher Q?<P> <P>------------------<BR>Norm


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Thu 05, 2004 9:25 pm 
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Location: Woodland Park, N.J. 07424
I agree that some sets are station deaf. I have an AA5 Silvertone that I replaced every capacitor, resistor and IF can on and it will not perform well at all. I have found that the simple sets with the lowest parts count perform remarkably well. My Mototola's and RCA are some of the best when it comes to receiving stations. I have a Packard Bell that is outstanding with very few components in its circuitry. I suspect that some chassis may have been wired wrong on the assembly line. I have compared several chassis that were the same but showed different changes in the wiring. <P>Wayne<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Thu 05, 2004 9:43 pm 
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Location: Detroit, MI USA
Even on the older radios from the late 30's and early 40's using the air core IF's, good sensitivity is possible. Some of those sets are excellent performers. One that comes to mind in particular is the Detrola 147, whose front end design was used in many other Detrola products around the same time. While not an AA5, it has only 7 tubes including a phase inverter and P-P output. If you were to eliminate those you would still have only 5 functional tubes in the circuit. It proves what could be done with a relatively simple circuit. This set used a preselector stage with no RF tube, but a 3-gang variable cap and an extra set of coils. It is a hot performer, and can pick up stations all over the dial at night with only about 6 or 8 feet of antenna wire.<P>My friend who was the manager of the coil winding department at Detrola for almost the entire time the company was in business swore that the differences in performance from one brand of radio to the next was all in the RF and IF coil design.<BR>He felt that you could take 10 chassis all the same, provide a schematic that could not be altered, and have all components except the RF and IF coils already installed. Then give them to 10 different radio companies to have their engineers put coils in them, and you would end up with 10 radios that would perform totally different.<P>Their engineers also used to play around with their competitor's designs, taking a chassis from a current model of some other brand, and redesigning only the coils. He told me they found some designs that were already really good and could not be improved upon, but many manufacturers were using coils that were off-the-shelf from an outside supplier, rather than custom designed for the particular circuit, and those sets were easy to improve just by making a different set of RF coils. <P>This seems to be a lost art after the late 1940's, and especially by the mid-to-late 1950's most manufacturers apparently did not care whether the performance of their sets was the equal to the competition or not.<P>------------------<BR>Dennis


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Thu 05, 2004 11:24 pm 
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Dennis, I tend to agree it has to be the coils, as the Delco I mentionesd has the best 5 tube performance so far, and it has a unique IF design..one, I for one, have never seen , but makes sense..if one IF stage at 455kc solves the selectivity issue, why not go for more gain? The 2 IF trans idea may have come, as a holdover, (we always do it that way!) from earlier early 30's low freq IF(260kc and below),where images were still a problem..at 455, with hiQ IF that may be much less, especially in a relatively low gain AA5; As far as ferrite or powdered iron cores go, it is my understanding they are far more lossy than air cores(inherent hysterisis losses) but probably more predictable and cheaper to make than variable C type IF, as far fewer turns are needed, due to higher u; a lossy IF core would increase bandwidth and reduce gain, (like a resistor across the IF coil)so maybe two IF trans are needed again with ferrite to get back selectivity? All of this says that IF's should be closely designed to the circuit, as Philco two IF stage designs(3 Transformers ) must have to open their bandwidth so as to not cut too much(probably too sharp,with three in a line (six tuned circuits)of "two IF trans" design transformers. Those Philco dual triode converter,two IF designs are also among the best on AM...another way to attack the problem. Also noted that 6BA6 (12BA6) has almost twice the Gm of a 6SK7/6D6/78, so mini tubes ought to be better, but air core IF's ought to be better,too..maybe that is the trade they made..more tube gain with mini's offset trans losses with ferrite. I know 50's Hallicrafters(?) went nuts on this, with their bulletproof main tuning cap and air core IF, I think some high end ham radios even had little air core tuning caps for the IF stages. Probably the best track?? I have never ever seen a Zenith perform as well as a Philco, when matched for sale cost,(sort of equivalent models)and especially best model vs best model... and I have done a lot of Zeniths, too.One I remeber had the push pull 6L6 set up,huge speaker, big fancy black front with about 6 wooden knobs, yet turning on a single light dimmer made it scream, while a Philco next to it had just a faint buzz..In the context of all this, it seems that thin, non litz wire is the worst way to go, followed by "3 wire litz" yet lots of radios do nothing else on RF/converter coils, especially..Thicker wire ought to give a little higher Q and easier to handle ,too. Bigger coils give higher Q ,too. I don't umderstand the obsession with #36 and smaller wire in radio coil designs..WHY?? Curt..with you 100% on that variation. I had a 1960 Dodge with one of those Mopar hybrid tube/transistor radios in 1960; (12V tube RF/IF, transistor out audio).I could listen to WPTR, the hot rock and roll station of the day(Albany) in Boston riding around all night, but none of the radios in my house could pick it up..a 50's RCA "Golden Throat"AA5, a 10 Tube (mini tubes)GE AM/FM console with a huge AM loop,and a Capeheart record player/radio would be full of static over the station,or nothing..yet the car radio was strong and clear..lots to think about here.. John..PS, maybe Delco IF's will fix Zenith woes...no one will ever hnow(smile)PPS Dennis ,I agree that preselector, or dual tuning on the first stage helps a lot,if the radio has enough gain afterwards .The Philco ninety has a 4 gang cap, with that design and an RF stage, and is quite good; however the cap is made of galvanized iron , which does nothing for the Q. This, despite early Philco TRF's that have BEAUTIFUL 4 gang caps , with brass plates, all soldered to the main brass shaft.Different guys win the arguement in different years, I guess..<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Fri 06, 2004 2:38 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 205
Location: Tucson, Arizona
Many of the of the sets with poor performance in the bottom half of the band can be greatly improved by replacing the non-adjustable oscillator coil with an adjustable one. This allows you to track the oscillator with the resonant point of the loop antenna, by "rocking" the tuning capacitor on a signal at 600 Kc while adjusting the oscillator coil for maximum signal. <P>This adjustment is standard on more expensive sets; it must be purely economics that a manufacturer would leave out the oscillator slug on an AA5.<P>This may explain why the VC plates are bent on some sets - perhaps an attempt to correct the misalignment? The problem is, bending the plates permits only a small amount of correction, which may be insufficient. An adjustable oscillator coil allows you to zero in exactly on the correct alignment.<P>------------------<BR>Bill S.


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Fri 06, 2004 2:47 am 
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I remember the comment an instructor at Valpo Tech said about Muntz TV--they copied circuits from RCA, GE, Motorola, Philco, etc.<BR>Then, they clipped out components until it quit, and then replaced that component--on to another circuit etc. Me thinks that is the same for a lot of wannabe AA5's.<P>Just my humble opinion. :-)<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Fri 06, 2004 5:08 am 
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Location: Cleona, PA
I've been able to get good results on some AA5's by bending the antenna section plates. Align the set the best you can first, then with a wooden or plastic stick carefully bend each section in turn for maximum volume as it meshes with the stator, tuning to a weak station in the range of each bendable section. <P>Reece <P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Fri 06, 2004 5:12 am 
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Peter Bertini wrote:
<font>quote:</font><HR>Originally posted by wvsaz:<BR><B>Many of the of the sets with poor performance in the bottom half of the band can be greatly improved by replacing the non-adjustable oscillator coil with an adjustable one. This allows you to track the oscillator with the resonant point of the loop antenna, by "rocking" the tuning capacitor on a signal at 600 Kc while adjusting the oscillator coil for maximum signal. <BR>.<P></B><HR>
<P><BR>The low end is the critical adjustment, since the RF antenna selectivity is appreciable, and even a 10 or 15 kHz error in tracking will cause signal attenuation. Another trick is to set the IF frequency for best sensitivity at the low end, and then rely on the antenna trimmer cap for aligning the high end of the dial, where things are much less critical and adjustable.<P>pete<BR><P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Fri 06, 2004 5:21 am 
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Location: Vieques, PR, USA
hehe, the old Muntz story. :-) I suspect that such is true for many circuits...<P>Your basic AA5 can't vary too much as far as circuitry but the quality of components, like the Q of the coils can vary greatly. Q not only implies selectivity but also less loss (greater voltage gain) at the tuned frequency.<P>Add me to the list of those who note dramatic differences among AA5 sets apart from simple alignment issues. You may be able to tweak tuning cap plates to get a mediocre one to be a better one but some models are just plain better out of the box.<P>I'll single out the Northern Electric 5000 'Rainbow' models as being consistently good performers. I've been thru four of them and two of the four were conversions from battery to AC which meant 're-inventing' the loop for the input stage.<BR>The Truetone (Detrola) 724, although not a classic AA5, is one that performs equal to a set with an rf amp stage although it shouldn't :-)<P>And most people snicker at the performance of a 3 or 4 tube set but I have seen pre-war 3-4 tube European sets that will easily match an AA5 performance-wise.<P>Now when you stick a tuned rf amp stage in front of the basic AA5 you have a kick-butt radio! Being in a radio 'fringe' area with few local stations I notice (and appreciate) the difference immediately.<P>-BM<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Fri 06, 2004 10:27 pm 
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Good to hear I am not alone; I especially agree with the statement that you can tell it's a good one or a loser, the minute you first turn it on,and that while bending the plates will improve it, the difference is not a great deal, compared to the variances we see.. I would leave the plates alone ,as there is absolutely no reason that would change if the other alignment points are right,(not always the case, once the golden srewdriver has been in there) and you can make it a lot worse by fiddling. The oscillator coil comment at low end really intrigues me, as I think that is critical..That is the reason to be sure the plates are in sync with the dial setting(which we then use later to set the high end trimmer, and that FORCES where the antenna is resonant to at the bottom, compared to the oscillator, at the low end..could force it to be in the wrong place!) I read in a Philco service bulletin about some kind of tuning wand Philco sold that had a brass end and a ferrite end..putting the brass end in lowers L of the coil, ferrite end raises it..I NEED ONE OF THOSE!! Anyone ever see one? Good item to sell!!another way is to slide a sheet of polyethylene (?milk bottle piece)between the cap plates (or mica ,even better); that raises C and tells you if bending will help,or reducing L will help,(turns on your home made loop antenna?) or closing the cap more for that dial position will help.(or opposite all of those, if it gets worse); related to the osc tracking at the low end, the plates on the design of tuning cap osc gang that are smaller in size than the antenna also have a non linear curve built into the shape to track the antenna ; this became necessary when the low end trimmer went away(on those,all the cap tuning plates are the same size) I can see where the osc being "off that pre engineered curve" will result in terrible performance somewhere on the dial. The osc coil itself then must have been very closely designed to give 1005mc (550 +455) at the bottom point, with gang closed.That may be a reference freq point to check with counter??The upper end you can fix with the trimmer, the lower end you are stuck with as it is , and if way out(15KC) it will never work.also lets you set osc , and then fix antenna to resonate at 550, so you start out right at least. if both are screwed up. Exray, did you ever find one of those 41-48 philco with the low noise converter(two triodes) and two IF, vs the tuned RF stage? the tuned RF stage and it's tuned coils add to the BS we are describing..now you have 3 variable tuned circuits; as Mr Detrola says, it must be all in the coils,especially the precision with which they are made and matched;That is the problem that kept 3 dialers alive so long ,and we still have it, more or less. Norm's comment about improved performance from newer IF transformers is also support of that(something punts inside IF trans), or some other form of degradadtion going on inside the IF trans. The Zenith issues may be just that ..same problem that cause breakdown+ noises, may wreck IF throughput/gain as well, and be quiet while doing it.(mica becomes conductive ,or lossy?Poor quality mica= low Q, losses in signal?) The data you guys present sure points to wide variation in Zenith overall performance (my experience so far is it is all bad!), but maybe they just did not know how to make good IF transformers that last(Could be?); Any Zenith pros out there ought to try Mr Detrola's idea of another variable mica trimmer outside the can, and disconnect the factory junk trimmers. You should be able to solder those right to the tube pins underneath, and set up IF there. Anyone have any idea of the range of usual 455kc IF trimmer caps? We can figure this variation in performance out...'<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Fri 06, 2004 11:52 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34326
Location: Sandpoint, IDAHO 83864
You sure bring up some interesting points! I know the tool you mentioned and I used to have one that was made by GC Electronics. Cost a couple bucks, but that was thirty years ago. One can be made easily with a plastic drinking straw, a small section of brass and a ferrite core out of an old IF transformer or loopstick antenna. My original GC tool seemed to have grown legs and wandered off to greener pastures, so I made up my own a couple years ago. I had some 1/4" diameter brass shafting material ( I use it for drifting the sights on my rifles). I glued it into one end of the straw and the opposite end, I glued a bunch of iron filings (from the shop grinding wheel). I suppose it would work just like the ferrite. Worked fine and sure takes the guesswork out of alignments. All you have to do is to stick one end at a time into the coil and see if it improves or destroys the output.<BR>Curt<P>------------------<BR>Curt, N7AH


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 12:04 am 
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Thanks for the info ,Curt. we can figure this out! I am not sure filings will work as well as ferrite, (the grains need to be ,like ,microscopic)and it probably needs to be 1/8" to fit in some of the coils, but I congratualte you on trying to make one! And if it works only marginally, it will do the job! There must be someone on the site that knows where to get 1/8" ferrite rods, maybe an inch long;brass is easy(old brass screw), and a plastic soda straw ought to be perfect. Now ,what about other things that make IF's die out? Wire insulation leakage or deterioration, or moisture come to mind? Anyone can confirm Mr Detrola's experience with Zenith IF' s dropping away due to cap problems inside?<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 12:06 am 
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You know, the more you think about it, if something is dying out in the IF coil winding, the osc coil may be similarly affected, changing frequency a little, or losses may make it tricky to oscillate on short wave bands? <P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 1:42 am 
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Location: Tucson, Arizona
I suspect that the wax the coils are dipped in, hardening after many years, causes the inductance to change just enough to change the alignment. This may also explain why the IF transformers are often out of alignment, even on sets no one has tampered with.<P>------------------<BR>Bill S.


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 2:09 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34326
Location: Sandpoint, IDAHO 83864
jgrady- what I have found is that the tool, even thou it is about 5/16" diameter, still works. You don't have to insert it into the middle of the coil. I have found that just placing it adjacent to the windings is usually good enough to provide some sort of indication.<BR>Curt<P>------------------<BR>Curt, N7AH


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 2:22 am 
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bill, I am starting to wonder if it not the IF but the oscillator coil that changes; then if someone (WHO would do that?)tunes up the IF with the trimmers, to max out at a certain freq station on dial, with slightly off freq oscillator, the IF will be peaked at wrong freq for proper tracking; I admit to tuning up IF on a station. maybe we should always, always use sig gen at 455, like the instructions tell you, or at least check IF freq is correct at detector with counter..a good one! I know this particular problem drove me nuts on a Pilot FM tuner (problem was bad/partially open osc trimmer) but someone had adjusted all the FM IF's and RF /antenna adjustments to "work" ,which they did at one end(about half) of the FM dial only,and the dial pointer was moved around to make the indication somewhat right, at one end. THAT was a party to find; mainly because counter only went to 100mhz, and barely did that. Same problem might happen on AM osc coil?? Maybe we are getting somewhere with this thread.<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 4:23 am 
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Comments...<BR>peaking IFs by ear is a sure way to screw up the alignment in general. If you happen to get lucky and be close to the correct freq then its fine and if you don't have test equipment you can always check the difference by finding the LO signal on a second radio. I've found 'ear peaked' IFs over 100kcs off before and there's no way the front end can track with that sort of error.<P>On IF xfmr caps. The 50s Zeniths are notorious for their bad mica sandwiches. Several things can happen here - and incombinations and varying degrees.<BR>1. Leakage between input and output due to silver migration.<BR>2. Bad physical connection due to the silver oxidation.<BR>3. The silver can simply 'go away' leaving the cap value below what it should have been. This means pushing the limit on the coil's slug adjustment and of course by then the Q of the xfmr is out of whack.<P>Oscillator coils....One set, the Philco 89 is notorious for a osc coil form that absorbs moisture. But I have seen it to a lesser degree in several other sets...enough so to where I keep the yf's hairdryer handy to do a bit of drying when I find an osc that refuses to track like it should. Sometimes it helps, sometimes not, but I've seen it work often enough to make it a reasonable suggestion of something to try.<P>When you look at some of the higher end sets, particularly old ham gear, you see good quality coils and trimmers, often ceramic coil forms. My GE A-82 with the Sentry Box was a masterpiece of fine radio engineering...noteworthy that it was also marketed to hams. <P>All the good engineering aside, some of my best performers have been ultra cheap sets that defy logic. An example is a little 5 tube post-war French set that I have. I like to DX on longwave when the band is open. About a year or two ago I was fiddling with this little set and was hearing several of the European BC signals on LW. Wow, that was the first time I had ever heard them that strong. So I went thru every other LW capable set that I had at the time and NONE of them received squat...with the exception of the GE A-82 previously mentioned but it did nowhere as well as the French set. Had the little French guy been a "nice" set I could accept that but it actually is a rather crummy little set as far as quality goes. So crummy that the SW band has two sets of markings on the dial..one calibrated for the main signal and the other calibrated to the images! Seriously!<P>I wish I could explain such oddities but I can't.<P>-Bill M<P><P>------------------<BR>


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